see if you can obtain a waste and overflow by Mountain such as the mod#BDR20S22-2 it is cable operated so there is little or no adjustment,can be gotten in a variety of finishes,good for tubs 12" to 22" ,is made of plastic so it will never rot and can be cut to size easily with a hacksaw

Basically there are two types of waste & overflow kits.

If your finished tub will have a 12"x12" access hole,eihter through and adjacent wall or up through the floor from underneath you may use the common waste & overflow kit which has an overflow body with a long tube attached that makes the vertical riser from the overflow down to the Tee.

The top of the Tee has a slip joint fitting so the tube from the overflow can be cut to length to fit tubs with different depths.

The side opening of the Tee also has a slip joint fitting so the waste arm from the drain shoe can be adjusted for length. (Note: the drain shoe is the casting that fits directly under the tub drain hole)

The Tee has an extended tailpiece which then drops down to the P-trap.

The rough in fittings are universal however you will need to chose which type of drain stopper you want. They have the cable type, the wire rod type that connects to a lever on the overflow trim cap. a toe kick type which is opened or closed by tapping with your toe, or a lift & turn type that fits in the drain opening and requires lifting and turning it by hand.

You will also need to chose which type of finish you want on the metal trim parts to match your tub spout and faucett handles.

If your finished tub will be fully skirted and there is no access panel the code requires a "Glue In" type waste and overflow kit.

The glue in type kits will have a cast overflow body, a tee, and a cast tub shoe. The installer then custom fits the connecting lines from standard schedule 40 DWV grade pipe and glues it in place. This type of waste & overflow also requires a glue-in type P-trap. These kits are also available with the different types of drain stoppers mentioned above as well as a broad choice of metal trim to match your faucett & spout.

The advantage of the glue-in type is that all joints are glued permanent joints so there is little to no chance of a leak once it is installed.

Although it is rare today, there still are some local codes that require all metal DWV piping. In those instances there is a tubular brass type waste & overflow kit available that is fitted the same way as the glue in type, but the brass joints are all soldered.

I can't thank you both enough for all of the information! I was so frustrated, and thanks to your helpful responses, I can get the pieces ordered.

I'm dredging this up so I can better understand.

Can you give me an example of a cast type versus the common type? (I'm planning a Kohler expanse 1118 tub--*could* have an access door, but I'd rather not.) Is the access door required permanently, or just during rough in?