I changed mine out,it might not pass code but it pleased me and solved the smell problem.The work I did but was quite time consuming and a lot of thinking envolved.

The conversion was done by myself, I got the tank from Camping world and
got the largest that would fit in the space that was available ,its a 20 gal
size but got to thinking later I could have went with a smaller one as the
black water is never used all that much.
 I vented it from the top side of the tank, first into the vent line for
the sink and other units but when it was folded there was an odor inside on
opening so I disconnected made a U turn and took it down thru the floor into
the outside with a screen caped to keep the mud daubers out.Be careful going thru the floor not to hit wiring etc.This is a 1 inch
vent pipe, and so far it seems to be working alright.I connected to the cold water line in the bath tub which is close, I try to travel with
both tanks empty to avoid as much problems as possible and to keep the
weight down.
 The longest trip we made was to Brownsville Texas from home here close to
Nashville,Tn.it was around 2500 miles round trip if I remember right and
things went well.
 The reason I went with a regular flush commode was we didn't do any dry
camping and I didn't like the odor put off by the chemical  and you had to
charge the 12 volt one with a bucket or pan which was no hard job ,the smell
was the main reason.
 The recirculating one cost over $400 bucks and the replacement cost is
close to a $100 for commode + tank around $100+ pipe and misc supplies
I just sold the TM due to age and health.
                                         Jim E