Convert water tank to holding Tank

[Bar Harbor]

I recently purchased a 1974 Catalina 27. It doesn't have a holding tank. I don't know what the P.O. did on the boat, I don't think i want to know. We do however have an old, dirty water tank, which is undrinkable, without a tonne of work. I was thinking i could just cut a couple new holes, and make it the holding tank. None of the new tanks i looked at online mentioned anything about special coating inside. Any advice?

 

[Bob]

What About Pump Out?

I do not think thats a bad idea, but what about pump out? I do not know if your referring to the settee water tank or the one under the v-berth? If you have both the fill ports on deck are just inches apart and if intend on making one of these tanks a holding tank these two deck ports would be too close for my comfort! Take a look at the International 30 Association Website (resources to sailing web sites to page 2 to 30 Association to technical library and owners manual plumbing schematics. Just where is the potable tank on your model? As for the tank itself as long as its vented for expansion then the fiberglass should be okay, but I am no expert. The present vent system for the waste holding system is thru the stanchion on the portside near the head. Therse are still available as replacements, but one can be installed thru the upper hull just as well. Bob