Hi Plough, I didn't put in soak holes in the end. I did what you described without the drainage pipe. It drains out into the earth through the pebbles. Doesn't spill over the pebbles - a bath drains quite slowly and the plants around it loves the moisture. I saved about $1k buy doing this.
I'm really glad I changed my mind regarding this but it does depend what type of soil you have. Clay would be an issue IMO.
