I need a bit more information before offering any advice... How many toilets?* Where are they located--at opposite ends of the boat? Or closer together?* Make/model/age?** Hoses--age? Brand (should be on the hose)? Smelly?*
I see you're not in the US...looks like you'll mostly be in the Med. Will you also need a gray water tank?* US regs prohibit combining black and gray water in the same tank...don't know if EU or ISO does too, but I strongly recommend against it because gray water tanks are MUCH more difficult to manage than toilet waste tanks...let's keep 'em separate if you must hold gray water.
*How reasonable (or not) is it for you to buy from UK sources?
Even before knowing the answers to those questions, I can tell you that you do NOT want a bladder tank for waste holding.* And I'm not all that crazy about the engine room as the location for a waste tank, for several reasons--difficult to vent to keep the tank aerobic...heat can be a problem...and the hose runs from toilet(s) to tank can be a lot longer, and more challenging and convoluted than they'd be in a better location.
As you may or may not know, this site is about to go down while being switched to another web host, possibly for days or longer...so if you want to continue the conversation during the "break," just send me an email (you can do that from my profile)...NOT a private message, EMAIL. I'll be glad to help you sort it all out and find good sources.
-- Edited by HeadMistress on Tuesday 27th of March 2012 09:20:37 PM