Leveling seam sealer w/ dispenser?

Yeah, you're looking at $50+ for one of those dual piston guns. I can also tell you that trying to dispense the product through a mix tip without the proper gun is a bad idea.

As suggested, I'd look into borrowing or renting one from a shop. I have a friend in the supply biz and he was able to hook me up when I've needed one. By the way, I've tried different products and found Lord Fusor #129 worked best for me on the drip rail.