My first smoke tank was an after-market windshield washer tank with integral pump, plumbing to each exhaust pipe, and wiring to the switch on the power lever.  I isolated / mounted the tank on the upper left motor mount tubing, with a couple layers of rubber strap.  I routed the clear tubing to a Tee fitting secured in rubber, to the engine mount, then used 1/8" brass tubing to each of the fittings in the exhaust pipes.  I laid out the route of the tubing, marked the pipes, and removed both exhaust pipes.  I cut a 1/8" pipe coupler in half, radiused each half to the radius of the pipe, and oxy / accy welded them to the aft pipe of each side.   After welded, I drilled one #60 hole through the exhaust pipes.  I placed these holes toward the bottom edge of the fittings, theorizing that if oil would lay in there it would gum up.  The switch is a push on / push off button, that is mounted right to the throttle handle.  This location allows me to work the smoke without taking my hand off the throttle.  I originally thought it would only smoke good at full power, but came to find I don't need much over 1/4 throttle to Smoke 'Em Up !!  I can smoke 'em while taxiing, without any problem !!  My exhaust pipes point down and away from the fuselage, and even when all the oil doesn't vaporize, the fuselage hardly gets anything on it.        I had a couple of squawks on the system, that I have taken care of.   1.)  I mounted the tank at about the same level as the fittings on the exhaust pipes, and it always dribbles out the pipes, with a little bit of smoke as a result.  Over a period of a couple of hours, it will drain the tank, but I usually 'Smoke em up' before that happens. 2.)   When I ran the tank empty, and refill it, the pump would cavitate because of the way the line ran from the bottom of the tank to the pump, and I would always have to prime the pump, by blowing in the top of the tank.  I got some strange looks from folks, while I performed this operation !! 3.)   The tank was too small.  It only was big enough to do about 3 smoke runs.  I would like to put about a 5 gallon bucket up there on the firewall, but I don't have enough room !! 4.)   I had to remove the top cowling to re-fill the tank.  I'm building a new tank out of fiberglass / West System resin, with a fill tube out to  the right side of the cowling.  I'll mount it lower on the firewall.  This will take care of all the squawks. 5.)   I now have been using the new smoke tank, but I had a small leak in the tank.  I used West Systems resin for the fiberglass tank, and evidently I didn't get the seam sealed up good enough.  I've never had that problem when I used polyester resin, but it kicks very quickly.  The West System gives some time, but it is also quite a bit more expensive.  The leak was repaired, and I haven't had any problems with the smoke system.      I was buying the cheap Baby Oil at Wal Mart, I think it was a little over $1 for the big bottle. I got some strange looks, when I checked out with 8 or 10 bottles of the stuff !! That's the best way to buy it when on a big cross country flight, because I don't like the thought of carrying a big supply of oil for smoke. I since bought a 5 gal bucket of Edcot Light White Mineral Oil, item #47106-05, from Hampel Oil Distributors, here in Wichita. It was $30 for the 5 gal. They told me it's what they sell to the Airshow Pilots. It still smokes pretty good, but it seemed like the Baby Oil from Wal Mart smoked a little better, and it smelled real good to the crowd.      When I built the second tank, I had to figure the dimensions needed, and used a cereal box to make the male mold. I think it was something like 12" wide, 5" long, and maybe 8" high. I made the bottom of the tank taper to the center, where the outlet is. I made it in two parts. I used fine cloth so it would lay down in the corners better...heavier cloth doesn't want to lay down in a corner, and keeps trying to straighten itself back out before the resin cures. First, I covered the cereal box with the clear packaging tape that epoxy or polyester resin doesn't adhere to. Then taped it down to my steel table, with plenty of flange surface where it sat on the table. Covered 5 sides with 3 plies of fine cloth, including a flange all the way around the perimeter where it sat on the table. This gave me a surface to bond the two pieces together, as well as a flange to mount the tank to the firewall. The other part of the tank was much simpler. Just made a sheet of 3 plies on the table. Then just fiberglass the two pieces together. For the filler tube, I used a paper towel cardboard, and just did a 3 ply lay-up around it, and cut and fit it to the tank, before bonding the back side on. I leak checked the tank before install, but a leak showed up after it was in service, in a corner, where the cloth wasn't quite wetted out, and seeped a drip about every 5 minutes. It was easy enough to fix after the tank was dry, then sanded & cleaned the area, and used 5 minute epoxy & small piece of fiberglass cloth. Ya gotta have all the cloth cut, pre-fit, and ready to go, before you mix the epoxy.  One drawback to mounting a smoke tank to the firewall, is that it probably burns, and it may add fuel to an engine fire.      The fittings you put on the exhaust pipes should probably be welded, not braized, and get them as close as you can to the flange at the cylinder head...much hotter there. I think mine are about 1 1/2" or 2" from the flange.   Just mark the location where they'll go, before you pull the exhaust, keeping in mind all the routine maintenance needed for the engine, like changing the spark plugs. I pointed mine inboard, so they are out of the way of most everything. Drill the #60 hole after the welding is complete in the lower portion of the fitting, so no oil will sit there next to the hot pipe after the pump is shut down. My exhaust pipes point down and outboard slightly, and I hardly get any oil residue on the airframe...mostly on the leading edge of the horizontal stab.      Caution about smoking in the wrong place...one time when I returned to Cook Field, and stopped to fuel up, a couple guys there at the pump said "Hey Chuck !! The Fire Department was here looking for you !! A neighbor called in and said an airplane that they saw was smoking, and were sure was on fire, and going to crash".

Here is a couple of shots of the initial Smoke Tank that I installed, but found that it was mounted too high, and dribbled out through the exhaust, causing a little bit of smoke all the time, and eventually draining the tank.   Also, I had to remove the top cowling every time I had to refill the tank.

Smoke 'em,  if ya Got 'em !!!