Looking at a boat with no holding tank

Greetings,
Well, it all depends on what size tank you will be putting in and where it will be located in relation to the number of toilets and deck pump out.
Another factor to consider is where the pipes/hoses will be run.
If you have lots of "wiggle room" installation should be pretty straight forward but if you have to get "creative" this will take more thought, time and expense.
Most, if not all, of the components should be off the shelf. I'm sure the Roamer owners on this site will be able to shed more light on your instal.
Peter

Depends on how big of a tank, what stage of completion the boat is (obviously the cost if you're gutted to the hull will be less than if you have a fine finish interior you have to disassemble parts of) how you do it, what you make it out of and how much work you do yourself.

If you make the tank out of Monel or 90/10 copper nickel and use the Trident hose, a y-valve, vent and deck fitting and get a Vacuflush head running on fresh water, it'll be expensive. All levels of doing it are available.

Installing a hoding tank isn't nescessarily a hard task. I would use a roto molded poly tank. Stay away from metal as the acid in the waste will eat away at the welds and the metal. There a companies on line that manufacture poly holding tanks, these tanks are pretty inexpensive compared to metal. If you want the capacity to pump overboard you can either get a manual pump or an electric pump. Plan on installing a deck pump out fitting. Hose is rather expensive ($10-$13/ft) get the fgood hose cheap hose will allow odors to permeate.

I would say on your size boat, it would be a rough cost of $1,000 or so if you do most of the labor yourself. You're going to need a tank (I'd recommend the plastic type ones). A deck fitting installed to pump it out at a marina. Marine sanitation hose to go from both heads to the tank. If you'd like to pump the waste overboard, you're also going to need a thru-hull fitting and seacock, a macerator pump, and a y-valve to choose between pumping it over or pumping it through the deck fitting. Also a remote gauge to show the level with a sender (if you so desire) or if you get the plastic tank you can see the level with a flashlight. If you have good access to everything, installation should be a day or so to convert it.

I too would recommend a good toilet like a vaccuuflush and also putting the largest tank that will fit.

I installed a 35 gallon holding tank under the v-berth floors of my 1967 Connie. Tankdepot had the best prices--there's a 35 gallon tank (Part: 85-1525WH) for $125. 1.5" PVC pipe doesn't have problems with smells and costs a ton less than hose. I only used hose for the two feet or so for vibration isolation. This setup was recommended to me by the now-retired commandant of the Philly naval yard, whose got more marine engineering degrees than I care to count. I haven't had a single problem with it in three years. I used the original heads and got a nice, stainless deck fitting from Defender. I think the whole thing cost about $200, and I did it in a weekend.

On my 46 Roamer there's tons of space for tanks, much more than the Connie. It should be a snap for you to put in.

When the black tank was installed in my '60 35' they put it directly under the aft hatch which I thought was a poor location. You always had to climb around it when getting around down there. I moved it forward some between the aft hatch and the center engine compartment hatch which made it a lot easier to move around. I then installed a sliding battery tray for my house battery bank above it that will hold 6 6volt golf cart batteries.