Holding tank access port?

What is the minimum size access port that would be useful in a holding tank? I would think the bigger the better but I don’t have much room on top. I assume it belongs on top and not on the side? Second, what type of port is best to install? Can’t imagine it is one of the spin in spin off types used topsides?

The so-called "standard" size is 3", but you can get 'em up to 10". You should be able to find the one you want here: 3" inspection ports etc


No sealant needed...a rubber gasket under the flange and an o-ring on the cap keeps it sealed completely.



--Peggie

I am not sure I would want one in my holding tank, I would be afraid it might leak. Maybe someone knows of one that will not leak. Let’s see what everyone’s says.

Peggie beat me to it.

Greetings,
Mr. fb. The dip tube in our holding tank (40 gal. aprox) sprung a leak last year necessitating a replacement. The tank is triangular and is in the hull right in the bow. Tank is FRP. The access hatch is aprox. 10"X10" (on top) and was plenty big enough for me to maneuver tools and replacement parts inside. The hatch is a FRP plate 3/8" thick held on via nuts and bolts, the bolts being held in place integral with the top of the tank. A well greased neoprene gasket effects the seal.

Thanks. Here is a picture taken during poopapalooza when the vent hose blew off and $^i# happened. As you can see, little room on the top that is exposed. Maybe on the rear of the left side. Not much room though. The remainder of the tank is under the generator. I could use the plate that is already there but would prefer something simpler than removing 8 bolts. Looks like the base on the 3" port is 5". I don't think that will work. Guess I'm stuck with the 8 bolt solution but its a pain and will lead to less frequent cleanings.

Greetings,
Mr. fb. I suspect you're overthinking the necessity for "frequent" tank cleanings. A healthy holding tank should not need to be cleaned other than pumping and flushing with fresh water. A task that can easily be accomplished without any disassembly. MY $.02.

RTF, as you know, your $.02 is worth $.04 to me. Will just deal with the bolts. You are right, just overthinking.

There is an overstinking joke in here somewhere I'm just too tired to go find it.

And...there you go!

I’m currently rebuilding my original setup. The eight bolts screw into a tapped metal flange INSIDE the holding tank. The hex-heads of the bolts are 10 mm. The threads are 1/4-20. I tried to think of a way to simplify the removal also. However, RT and Peggy are correct. If we take care of our holding tanks with regular flushing when we pump out, we shouldn’t have a need to open the top all that often. Keep it aerobic!

When I complete my rebuild, I’ll start another thread to “tell all” what I did.

Thanks Ray. Yours is a 1986 and mine an '87. Is yours a fiberglass holding tank? The flange is embedded in the glass, correct?

Yes, fiberglass. And, yes, the flange is embedded in the glass. The distance between the bolt hole centers is 2 1/8”. I’m using the space on the left in your photo (I don’t have a tank level sensor) to install the discharge hose from the aft head and the vent hose. The discharge and vent hoses will utilize uniseals. The suction hose with dip tube will use PVC bulkhead fittings.

The original GB fittings were copper tubes brazed onto a bronze plate (like yours). My copper tubes were dissolved away and the bronze plate was chemically changed to a brittle pos! Obviously GB didn’t read Peggy’s book! I’m using a 1/4” fiberglass sheet to replace the bronze plate.

Again, I will detail my rebuild in about one week, after I install and work out the details.

Edit: In the mean time take a look at the following:

http://www.trawlerforum.com/forums/attachment.php?attachmentid=82219&d=1540243001

Mine is a 45 Gal poly tank, it has a 4 maybe 6" opening flange and screw in cover. It is very handy, every once in a while we will stop at a marina with in slip pump out. I'll pump out the tank, open the inspection cover then bring a garden hose with a nozzle and give it a good pressure wash out through the inspection hole, then pump out again for a clean tank. That can all be done at the pump out station too if they are not busy, and a generous tip. (that hose is not the same one I use to fill the water tank)

Thanks. My cover plate is in good shape and the discharge tube had already been replaced by the PO. I had to replace the vent connection as it was rotted and blocked. Will rebuild and replace the whole connection plate as I am not 100% happy with the vent connection. Would like to add a second vent line for better cross ventilation as well as a second holding tank for the forward head. Would like to do all of this at once, to include a good cleaning of the tank, as getting to it and opening the plate isn't much of a fun Saturday. Hence my questions about adding an access port.