Slow leak in a DE filter drain plug


Well-known member
May 22, 2013
Dallas, TX
When I cleaned my DE filter recently and reassembled it, I noticed a drip-drip leak from the drain plug at the bottom. The filter tank has a plastic cap with a small O-ring in it. I tightened it all I dare with water pump pliers, but it still drips.

I just recharged the system with DE after end-of-the-season flushing of the filter screens, so I hate to have to break the whole filter down again and put another 12# of DE back into the system.

Here’s my question. Before I can take the cap off the drain, I have to relieve the pressure in the tank, let the water in the tank flow back into my drain system, and then when I remove the plug, I expect to lose some/most? of my DE material that will be in the very bottom of the filter tank below the lowest plumbing connection to my pump. I have no way to capture what comes out because the drain is only about 2” off the ground. How will I know how much DE to replace when I get the plug back on and the leak repaired?? Is there any way to estimate how much DE to put back in?

I plan to use teflon tape, be sure and clean the threads, and make sure the O-ring is not crushed. If so, I’ll replace it.

Thanks for any advice on how to recharge.


Mod Squad
TFP Expert
Platinum Supporter
LifeTime Supporter
In The Industry
Apr 1, 2007
Sebring, Florida
Before I can take the cap off the drain, I have to relieve the pressure in the tank,
There is no pressure in the tank unless your pump is running.......other than gravity assuming your filter is above the pool water level.


Well-known member
May 22, 2013
Dallas, TX
Thanks for the reply. My worry was not how to fix it, but rather how to figure out how much DE I had lost since the plug is about 1” off the ground and any slurry escaping goes right out onto the ground.

I released the pressure on the tank and let the filter tank water/slurry run back into the circulation pipes. I then unscrewed the leaking cap and it looked like about 1/2 gallon of slurry escaped, less than I had anticipated. I eyeballed a guess and figured I would need about a pound of DE to replace what ran out when I fired the system up again (6# required on this filter to refill it after a back flush, 12# to refill it after a full breakdown and cleaning).

When I got the cap off I found that there were some hard calcifications on the threads that I was able to remove. The gasket looked fine. It is less than 1 year old, and it had NOT been damaged during the cleaning and reinstallation. I wrapped the threads of the cap (it was male, thank goodness) with Teflon tape and put silicone grease on the threads. I then screwed it back on (carefully) and tightened it only “hand tight” not using pliers. I primed the system, fired it up, and put the 1# of DE in to replace what I had lost, and no leak!

I am assuming a pound or two of DE one way or the other in a 12# DE filter won’t damage the grids. Anyone with a different opinion, I welcome hearing from you.


LifeTime Supporter
TFP Guide
Jun 12, 2011
Don't worry a pound won't make a big difference. When you do a break down cleaning you know how much to use because you start with none and the grids clean. When you just back wash you use 80% of the labeled capacity, but that's just a guess. So it's not rocket science. It'll be fine.