Notice the white buckets sitting on the ground on the left corner.
When I first started this project I had a couple buckets but one of them had holes in it. Several years ago in my Tomato potting project I drilled holes in the sides and bottom to let the water drain so the root systems wouldn't drown. I have since decided a serious mountain garden was in order, so the bucket now is being diverted to water collection.
In order to seal the holes I used 100% clear exterior strength silicone , the kind that comes in a tube and is used in a caulking gun. I filled the holes both inside and out with silicone.
Time would tell how well it would hold.
Its been two months and all is well. The water has not seeped out, even when its been full for days at a time.
I also use this product to seam seal silnylon tarps, tents and packs.
If you have to patch or glue plastic, I recommend this inexpensive product. You can find it in the hardware section at Walmart. Apply it to clean dry surfaces and allow to dry and cure completely.