According to the 1988 C-34 Owners Manual (pg. 37), your boat should have one 43 gal. water tank aft and a 28 gal. water tank amidships with a 27 gal. waste tank also located amidships. There should be a pump-out fitting located on the deck amidships on the starboard deck) and a vent through one of the lifeline stanchions (just a small hole outboard and low on the stanchion, also amidships to starboard).
It is unlikely that Catalina Yachts produced a boat that was illegal at the time it was manufactured as direct to sea discharge of untreated sewage is and was illegal in US waters within three miles of shore. If your potential new Catalina 34 has no holding tank and does have two fifty gal water tanks, it is most likely an aftermarket modification thay you will need to reverse (at least partially).
Steve
Alchemist C-30T #4764 ('87)
Alchemist C-320 #909 ('02)
Alchemist C-380T #71 ('97)