The way I do is to use a water input tube for washer machines. I found them very flexible, not all of them, but look on the hardware store. Then I connect this to a regular plastic tube and I cut one end of the waser machine tube, then I put a soft plastic cup to cover the cut. It is not very thick, but easy to manouver inside and goes all the way.
Then I connect it to the tap, and when water is warm and good, I start to introduce it in me. I fill out my self with less than a quarter of warm water in 15 to 20 minutes. So it is slow.
When I fill full and my body said stop. I go to the seat and push all out. Then I repeat it again until water come out clean.
After the third time, I am able to put the washer pipe more than 40 inches in. Always with the tap on and water filling me very slow. I felt how it does travel inside me and how it does move through my belly skin. It is needed a little push in and out to pass the curve between the ascending to transversal colon, but it goes through it, then i felt how the tube is pushing from inside my crotch.
The Washer machine tubes are not longer than 42 or 44, so it need to be extended since it can go inside 40 in. Some time i found samll part of the tube outside me.
No man can give me this type of pleasure. No one of my circle know about it, so I want to share here.