The holding tank is 14 gal Nauta
bladder tank. Fresh water also bladder tank ~37 gal. Replacements available thru West Marine, Defender, etc. Cost ~$250 for 14 gal one. Probably a good idea to replace the holding bladder if original. I have a 1985 P303 and replaced both tanks about 3 years ago. If fresh water tank leaks - not too serious, but, if holding tank lets loose, you're in deep dodo, pun intended!