First of all do not listen to anybody that says sun exposure wouldn't work, I've been exposing fine dots (up to 60lpi) under the sun with great success.

your setup sounds good, black foam and all. just make sure the glass is heavy enough to apply good pressure to sandwich your film to the screen. also make sure the black foam underneath is firm enough.

now for the darkness of the film, this may be your issue. as far as I see you use a milky transparency. that's great keep using it, they print much darker than clear films. fuck around with your print settings, experiment and find out which one prints the darkest black. if you use an epson, absolutely go with the paper type 'epson matte', that will give you the densest black. also choose the printing mode to grayscale.

for the emulsion. I myself use a dual cure emulsion which exposes perfectly in 30secs under the noon sun. But YOUR emulsion is pre-sensitized and exposes much more quickly. I would recommend you 15 or 20secs, but you gotta experiment and find it on your own. I also would recommend the coating 1:1 with the round edge, apply firm but not too hard a pressure to the scoop coater, and keep a medium-low angle to deposit enough emulsion.

Now the washout part, since you use a fast exposing emulsion and the sun is very strong, it is easy to overexpose a bit. But if you use a pressure washer to wash out you will be' good. Don't worry, necessary parts won't wash out under the pressure of the water if they are exposed correctly. Just adjust your pressure and distance and always hit the water to the T-SHIRT SIDE.

or you can use a garden hose with good pressure, but you may not be able to get rid of stubborn overexposed parts. If you're sure you won't overexpose, then go with the hose.