Done a search but didn’t come up with anything. Did anyone have luck repairing a cracked plastic tank? Mine is a 79 IT 175 with about a four inch horizontal crack at the lower waterline. Methods or types of adhesives? Thanks 

I’m thinking scuff it, clean with acetone, warm with heat gun and hot glue it.
Just thinking the hot glue might be fuel resistant.

How about a soldering iron and some similar plastic as a filler rod ?, I've done some good repairs using this method as it will melt the crack together.
Just look on YouTube for details.

I would buy another tank. Fire hazard being that close to your exhaust 

Got a tank on order for about two months. 

Took a pellet of hot glue and soaked it overnight in premix. The glue will desolve so that won’t work. 

I've used hot glue where it's been submerged in water and it holds, but I didn't think it would stand up to gasoline. I know a lot of people repair RV holding tanks with plastic welding, you might look into that as a temporary measure. I've never done it, but I think you can buy a kit fairly inexpensively.

Here's a guy just using a soldering iron, as Mauser suggested, and he cut off a little piece of donor material from a fender.

They make fiberglass repair kits for plastic 

If it was mine I would do both plastic repair and fiberglass on top for better protection until your new tank arrives 

Bought one of the rather expensive plastic welders from Harbor Freight Tools today. I’ll make a practice run or two on my old beat up quad.