Draining freshwater tank without using the pump

MHorn0817

MHorn0817

Active Member
May 16, 2021
205
Bowie, MD
Boat Info
1998 215 Express Cruiser
2011 260 Sundancer
Engines
5.7 Mercruiser Thunderbolt w/Alpha I
350 Mag MPI w/Bravo lll
I'm looking for a good way to drain my fresh water tank without using the pump. Asking because my pump strainer keeps getting clogged while trying to flush out my tank and lines. So I'm looking for a faster and easier way to drain the tank without having to stop every 2 minutes to pull the filter and clean it out.

On a 2011 260 Sundancer with 25 gallon tank.
 
Pull the pump inlet hose (shutoff the valve if it has one or you’ll have to work fast) and junction it to some kind of transfer pump. Harbor freight has some cheapies.

If you can only find a submersible pump maybe run the tank hose into a 5g bucket and use the submersible to pump out of the bucket.

last option would be to just let it drain into the bilge and see if your bilge pumps can pump it overboard
 
Those are definitely some good ideas. I appreciate it. Do you think it will flow enough to push every out with the wife of the pump?
 
I pulled the line off the inlet and used my small shop vac to vacuum the tank dry. Basically I put the inlet hose in the vac hose and filled the gap with a rag and it worked fine.
 
While on the hard, I adapted the tank's outlet plumbing to a 3/4" garden hose fitting, ran a hose over the side, used another garden hose to backfill the first hose, then disconnected them and let gravity siphon the tank. Depending on how deep your tank is compared to the top of the gunwales, you might be able to start the siphon action with a wet/dry shop vac instead of the backfill operation.
 
I thought about finding a hose to attach it to and just siphon and letting it drain that way over the gunwale. I originally thought to just let it go to the bilge and let the bilge pump pump it out.

I'm not sure what exactly is clogging it but I can describe it as a brown slimy substance.
 
All good ways above.

The water in the tank has sat for too long - either not treated originally or just plain sitting too long. Use the water on a regular basis - even if you just open up taps and run it dry - that keeps the water fresher. You can add some water fresh additive - or just a couple capfuls of bleach.

For now, after getting it emptied as best you can, put a 1/4 bleach in there and add about 5 gallons. Drive it around to slosh the mixture. Let it sit over night and then pump it out again. Repeat until you have clear water, then flush a couple times with straight water.

You'll want to flush all of your lines (including the HW tank) with the "clear/good" bleach and water mix, too. Do this before putting things away for the Winter. You'll probably need to remove and clean your aerators, too.
 
Thank you for all the tips and information. We are new owners of the boat and trying to go through it and make sure everything is how it's supposed to be. We did a bleach treatment which seemed to clean and break up alot of stuff which is now what is clogging the filter and we're trying to remedy.

That is another thing I have not completely found the answer to... How to properly drain, clean, flush, store the hot water heater. I see the actual drink on the water heater but have not messed with it yet.
 
MHorn0817 said:
That is another thing I have not completely found the answer to... How to properly drain, clean, flush, store the hot water heater. I see the actual drink on the water heater but have not messed with it yet.
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Hopefully, yours won't fall apart in your hands from lack of use like mine did! If you're using air to blow out the system, that valve will allow you to empty the tank in short order. If not, gravity will eventually do the job, but you'll need to allow makeup air in (lift the lever on the T&P valve). Don't get me started on the whole "blowing-out-the-system-vs-using-the-pink-stuff" discussion. That's in another thread If you opt for the R/V antifreeze in the system, consider either adding the water heater bypass or connecting the two lines together as discussed in the attached thread. Either way, you need to drain the heater first.
 
Nater Potater said:
Hopefully, yours won't fall apart in your hands from lack of use like mine did! If you're using air to blow out the system, that valve will allow you to empty the tank in short order. If not, gravity will eventually do the job, but you'll need to allow makeup air in (lift the lever on the T&P valve). Don't get me started on the whole "blowing-out-the-system-vs-using-the-pink-stuff" discussion. That's in another thread If you opt for the R/V antifreeze in the system, consider either adding the water heater bypass or connecting the two lines together as discussed in the attached thread. Either way, you need to drain the heater first.
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Awesome - thanks for posting that link bfore I started typing, Nathan! Super helpful! Horn, there are plenty of other threads about this, as well, if you wanted more reading material.

But, as noted, just drain it like you were probably thinking. You can run a short length of hose directly to the bilge floor, if you want. In case you don't know, the "T&P valve" that Nathan is referencing is pressure relief valve, just like on your home's water heater. Lift the lever to the horizontal position and it will stay there. It's the most direct way to "take your thumb off the top of the straw".
 
Awesome info and write up guys. I really appreciate it.
 
Yeah def flush with higher bleach concentration. You don’t want that solidifying over winter layup.
 
Absolutely. Just need to get it all out now, lol.
 
Last edited:
MHorn0817 said:
Absolutely. Just need to get it all out now, lol.
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Last year I used a compressor and blew all the water out of the lines after draining tank. It worked really well and going to do the same this year.

My tank drains pretty easy into the bilge after being disconnected from the pump vs using the pump.
 
Little Ducky said:
Last year I used a compressor and blew all the water out of the lines after draining tank. It worked really well and going to do the same this year.
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Did that the last two years with the boat, and have always done that with numerous R/Vs through the years. Antifreeze use is reserved for pouring down the drains to keep the P-traps from freezing, plus thinning-out anything left in the grey/blackwater tanks.
 
What I asked is so I can fix the problem (flushing and draining the tank to clean it out). Everyone is giving me answers and options to do so.
 
Wound up just removing the outlet hose and letting the pump , pump into the bilge and just had the water hose nearby and cleaned the filter a few times. Flushed the tank about 4 times this way (way faster then running through faucets) and tank is now fresh and clean and no more filter blockage. Just in time to winterize it all, lol.

I also drained the hot water heater. Drain opened right up and vent valve worked perfectly. I still need to bypass the water heater now and flush lines.
 
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