Doug, The toilet you are looking for is the Thetford 135. Originally, when Jerry designed the M-15 this was the model that he used to create the toilet storage well. Unfortunately, Thetford redesigned the 135 and it no longer fit the existing storage well. However there is a way of getting this model to fit the older M-15's. All you need is several gallons of boiling water and 2 beers. Here are the instructions to retro fit your Thetford 135: Place the toilet into the existing storage well. Open the toilet lid and toilet bowl trap door. Poor in 2+ gallons of boiling water. Close the toilet lid. Sit on top of the toilet lid, pushing the toilet into the existing storage well. While remaining seated, open one of the cold beers you brought with you. Begin drinking the beer slowly. Once you have emptied the first beer, repeat with the second beer. The softened plastic will reform itself to the shape of the existing storage well. After the water has cooled, the Thetford base will now fit you M-15 just like the original. Please keep in mind the current Thetford 135 has been redesigned........again!! And this time, I'm not sure if it will fit or not. I'm sending you the link of the previous model which will fit (will a little encouragement) in an M-15. At least the early models back in the 80's. Good Luck!! Skip M-15 #201 1982 M-5.5 #177 https://www.ebay.com/itm/Thetford-135-Porta-Potti-RV-Camper-Tenting-Portable... -----Original Message----- From: doug <doug9326@gmail.com> To: For and about Montgomery Sailboats <montgomery_boats@mailman.xmission.com> Sent: Mon, Jul 2, 2018 1:49 pm Subject: M_Boats: Porto Potti Hey, what do you use for a porta potty in your M-15. The space for one is so so small that I cannot find a single porta potty that would fit in that 12” wide space.