With 3 traps there are 2 traps between any pair of bowls. That's significant resistance.
With 1 trap the 2 bowls are simply plumbed directly to each other, no extra resistance between them.
In electronic terms:
----R1---+---R2----- | R3 |
versus
--------+--------- | R3 |
where R1&2 = trap resistance, R3 = waste pipe resistance Anyone that understands the basics of impedance can see which is more prone to one bowl filling the other.
Grow up. Youre not 13 any more.
NT