Gravity Holding Tank Won't Drain

[jzk]

Here is one way to deal with a gravity tank that gets clogged a little occasionally. If you have a Y valve that is plumbed like this. One position of the Y valve pumps the waste into the top of the tank. The other position of the Y valve allows the waste to go right out the thru hull. One trick is to close the seacock and to flip the Y valve to the wast out the seacock position. Pumping the head will then force water up into the tank through the bottom discharge tube that goes to the Seacock. 10 pumps like this before you gravity drain can remove debris that has settled at the bottom and is waiting to clog. Then flip the y valve back and open the seacock. You can generally hear if it is draining.

[delmarrey]

Gravity holding tank? Not sure how one would work unless it were well above the waterline.

The general construction should be a down tube into the tank to suck out the fluids with the ability to flush in clean water while its being extracted. Unless there is a macerator installed like on page 11 of the link below, I’m not sure I would want a fitting at the bottom of the tank!

I hope like hell, on a gravity tank, that the lower fitting doesn’t leak/drip.

https://www.nsboats.com/wp-content/u...on-Systems.pdf