"Timothy" wrote in message
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2 Never use a hosse end sprayer to apply chemicals/ fertilizer.
The water pressure in the hose varies and the amount of chemical/
fertilizer applied will vary also. Furthermore, it's quite possible that
you could contaminate your own water supply via the hose end sprayer. As
the water pressure varies, it can syphon the chemicals back into the
hose and into your house/well. If you must use a hose end sprayer, use a
check valve with it. Here's some more reading on the subject:

I don't know where you live, but where I live backfeed preventers are
required on all outdoor sillcocks. Also, it would take quite a siphon to
get chemical through a few hundred feet of hose back into your indoor
plumbing system...

It is VERY tedious to apply something like Weed-B-Gone with anything but a
hose-end sprayer, on all but the smallest lots...

-Tim