You dont need soak holes , dig a ditch 200mm deep in the lawn or garden (for free irrigation) put in drainage rock about 50 mm deep in the ditch then on top of the drainage rock (pebbles) put in the ditch about 8 metres of 100mm plastic drainage pipe (novafow) leading up to the outlet of the bath , cover the pipe with soil to level with the lawn , you may need to restrict the outlet a little but it will be fine.
