Rocket Mass Heater idea?

I recently read that really the only thing better for the mass in a RMH than cob is water. My idea is to use "8 metal piping routed through an old bathtub. It could be plumbed to a shower, laundry station, etc. Yes it would be larger than most would like but if it works I won't mind a surface large enough to sleep on!

Kevin Woods : It is really hard to comment without a picture or a sketch, but your plan requires cutting up of or into the bathtub ? this would not be a job for a neophyte welder !

I can not promise any answer that you like, behind a civil one, due your best, and stand the test ! Big AL !

Since all I have is a smart phone I'll do my best to describe my idea.
The J pipe would be located somewhere along the first 1/3 of the tub. This is so the exhaust pipe can be routed out next to the 55 gal drum using its heat to help draft. The pipe would lead out of the drum and loop through the tub filled with water.
It would be steam type pipe with a T for clean out. Yes, a clean out would require the water to be drained. Having a natural spring and planning to have a greenhouse will mean I'm not wasting water. All opinions are welcome. Have a blessed weekend Permies!

And no it would not require damaging the tub at all. Using its original drain to empty it and a platform to support the J pipe weight so the tub could be removed and repaired/resealed at any time.

Kevin Woods : there is a viagra commercial showing a couple in adjoining cast iron bathtubs with burning wood piled under and around the bottoms of the twin tubs enjoying
a sunset and holding hands ! It would be simpler to cob all around the sides of the bottom of the cast iron tub and have your hot exhaust gases channeled a cross the bottom
of the tubs and up the backrest!

A total contact area of 24 by 70-ish inches, and having the base of your exit chimney already constructed , cheaper and more surface area for effective heat exchange ! You
will need a wooden plank to sit on to protect your wedding tackle ! Big Al !

Lol!! All I have is a conventional modern metal bathtub but I think your idea would work with it as well. In fact it would have better access to clean out T 's using your suggestion.