The tubing is easy. About 3/8 inch outside diameter (o.d.) flexible silicone tubing works well. I mixed tubing types, and that proved to be a mixed blessing. The stiffer plastic is cheaper, but then I had to put in a section of silicone for the hose clamp. Next time I make one of these, I’ll just get all silicone tubing. It is very durable. I don’t know why I was in such a cheap mood the day I bought different kinds of tubing. Get about ten feet. Clear is good; you can see when the water runs out.
Also you will need some tubing fittings. Get 3 each 90 degree elbows: two to negotiate the lip of the bucket and one for the grommet connection through the splash guard. Get a hose clamp, and then something with some weight to it that will hold one end of the tubing down in the bottom of the water bucket. I used a brass T-block with a barbed fitting. It’s chunky enough to make a decent weight.
Attach the weight to one end of the tubing and put it in the water bucket. Cut the tubing so that an inserted elbow will just see over the top of the bucket rim. Cut a small section of tube (about 1 ¼ inches (3 cm) long) and fit it to the horizontal arm of the elbow. Insert another elbow in the free end and point the open end down. Attach the remainder of the tubing to the free end of that elbow. Slide the hose clamp onto the tubing and position it so that it is handy for a person lying on the board.
The end of the tubing will attach to the elbow that is fixed in the splash guard.