Anoldguy, that 9.5" x 2.75" dildo must feel great! I know from experience.
I have one very close to this size that I use in the tub too! It has four rounded bumps along its length, with the largest bump having a 2.75" diameter. With a bit of wood and a few screws I turned my big dildo into an awesome bathtub fucking machine. The rig I built consists of about two feet of wooden dowel with a small round piece of wood screwed into one end, and a bathtub width of 1x6 pine board screwed in perpendicularly to the other end of the wooden dowel. It looks like a 'T'. I can quickly secure any plug or dildo with a flared base to the small round piece of wood with a long strip of bicycle tube rubber.
When I put this rig on the floor and stand on the 1x6 board, the dildo is held stationary with its upward pointing head just below my butt. I can do hundreds of knee bends to fuck myself, but this is a lot of work. This rig was made for the bathtub.
To prepare for bathtub play, I first use a generous amount of olive oil to thickly coat all the moving parts: my back, my butt, my anus, and my rectum, which gets a big squirt of oil. The dildo must be thickly coated in oil too. To make things totally slippery I also pour olive oil all over the bottom of the tub. I carefully get into the tub on my back, and then slide all over the tub on my back and butt to get the oil coating everything. I'm soon bouncing off the walls of the tub like a hockey puck. I then grab the little fucking-machine rig and set its 1x 6 board horizontally oriented along the bottom of the front wall of the tub. I place one foot on either end of the board to press it into the tub and lock it in place. With my legs straight and slightly spread, the head of the dildo is held virtually stationary between my legs within inches of my anus. The dildo can only move a little vertically.
Next, I gently push my body forward with one hand on the back of the tub as my other hand guides the dildo's head into my anus. Then I use both hands to slowly push off the back of the tub to drive my butt forward until my anus slides down the whole 9.5 inches of dildo and bottoms out. For the last two or three inches of dildo I have to push off very gently and slowly to let the head of the dildo gradually open up my inner sphincter and slightly penetrate into my sigmoid colon. This is intensely pleasurable, as you must know. When the stationary dildo is completely inside me, my knees are bent, my feet remain over the 1x6 board at the front of the tub, and my hands remain on the back of the tub.
The fun really begins when I start alternately pushing off the back of the tub with my hands and pushing off the front of the tub with my feet. My back and butt effortlessly slide up and down the tub, and the dildo doesn't move. When I push back with my feet, my butt slides back in the tub, and my anus pulls most of the way off of the dildo. When I push off with my hands, my butt slides forward, and my anus slides all the way down the 9.5" of dildo and hits its base. My hands never touch the dildo. It takes surprisingly little effort to slide my butt very rapidly up and down the dildo. The pleasure is insanely intense. I always fuck myself faster and faster into a frenzy. I've come very close to a pure anal orgasm, but I've never been able to resist taking one hand off the back of the tub to grab my cock. That always triggers a big gusher in a matter of seconds.
SallyXX, I bet you'd love my little device. We could try different dildos on it until we get just the right one for you.