Another interesting idea of making a new BH smells good.
This idea was carried out before and pretty similar to those perfume garden.
The perfume garden method uses smaller bottle by this new idea is to use a larger container which can stored about 500 millilitre of "perfume".
The selected containers were not placed on the nesting planks but on the cement walls.
The best perfume, from my point of view, is the fermented raw nests.
Get about 3-5 raw nests (the dirties or broken nests) and soak them for at least 5 days.
Use about 2.5 litres of plain water for soaking.
Once ready drain the raw water into a separate container.
Take those soft nests ready to be placed inside those plastic containers that were screwed to a piece of 6"x6" nesting planks.
The containers should be about 1.5 feet below the nesting planks.
Insert the soft raw nest using a spoon or a pincher evently.
Once that is done you can pour water into these container so 3/4 height.
Cover the containers and make sure you drill holes on the covers.
The smell of these fermented raw nests will make the BH smell better to those swiftlet and they might feel less stress or more at home.
No guarantees but all you need is some good ideas.
Good ideas comes from Pak Harry
Best of luck to all who are creative.