OK. The Sealand 911 toilet and tank was discontinued. It was replaced by the Sealand 711-M28 toilet which is currently used in Scamp
trailers. The 711 tank will not work under your toilet without modification. (Threads can be found here on the modification.) The easiest thing to do is order a toilet and tank from Scamp
or go with a composting toilet. The 711-M28 tank comes in a RV version and marine version. The RV version has a bottom discharge, which you need. You should call Dometic to get the proper version tank P/N if you go to another vendor. The toilet and tank are ordered separately from other vendors but shipping is cheaper than Scamps shipping. But Scamp
can supply the proper drain pipe fittings you will need.