I created a version of this for the Domme I see monthly.
I purchased a vintage metal tractor seat (the kind with a pattern of ventilation holes) on eBay. I had it sand blasted and powder coated by a local shop - tractor red. No way it will chip or rust.
Attached the seat to 18" x 36" x 1" plywood that I painted with multiple coats of gloss white enamel. 4 stainless bolts hold the seat to the plywood, with a 2" hole under the already-there .75" hole in the center of the seat. This allows for the use of a variety of nozzles for impalement, with the connector through the center hole and connected to an enema bag, water jug or other liquid supply. The plywood panel has eye-bolts every few inches in an arc at each end, allowing for ropes, cuffs or other restraints to be used on the rider - for safety of course, like a seat belt, to prevent falling off. The bolts will also allow for suspension of the seat from overhead hard points - or even a tree or swing-set frame outdoors.
Silocone Nozzles makes a number of nozzles that are well-suited for this device, including the CRRT, the SPD Concave series (1.25" - 3.0") and the RTDL-DBL, and others. While colon tubes will work, the seated position pretty much guarantees leakage unless you have a plug/nozzle like these to prevent it.
Obviously, the seat can also be used for dildo impalement, electro-play, sounds and other amusements.