Will it work on plastic tanks such as a weed eater?

I used this in May 2020 on a Honda mower tank - the one that was recalled for a leaky seam. It worked. But in September 2021 it started leaking again so that was only a temporary fix in this case. Not the product's fault.

is this for external use?

it can be used as an external but intended for internal. i have vast experience with por15, they make an incredible exterior rush proof coating as well.

do I need to use this on a new gas tank I bought to instal on my car?

No, it is not necessary, especially considering most new cars have plastic tanks that won't rust anyway. Don't go through the hassle of? removing you're gas tank and fuel pump just for the fun of it!!

ASIN	B00B3HXCZ4
Best Sellers Rank	#13,678 in Automotive ( See Top 100 in Automotive ) #26 in Automotive Fuel Transfer & Lubrication
Brand	POR-15
Brand Name	POR-15
Color	clear
Compatible Material	Metal
Customer Reviews	4.5 out of 5 stars 3,293 Reviews
Global Trade Identification Number	00051491492164
Item Dimensions	7.1 x 7.1 x 7.6 centimeters
Item Form	Gel, Liquid, Paste, Silicone
Item Weight	0.01 Ounces
Item dimensions L x W x H	7.1 x 7.1 x 7.6 centimeters
Item weight	0.01 Ounces
Manufacturer	POR-15
Material	Liquid Sealant Compound
Material Type	Liquid Sealant Compound
Model	49216
Number of Items	1
Part Number	49216
Style	Compact
Style Name	Compact
Surface Recommendation	Surface
UPC	038514492165 680336041030 051491492164
Unit Count	8 Grams
Water Resistance Level	Waterproof
Water resistance level	Waterproof

POR-15 49216 U.S. Standard Tank Sealer - 8 fl. oz.

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