How long would it take to empty a hot tub using only a drinking straw?

Clarify Data Points: The bathtub size may be 6 ft * 6 ft* 2 ft- standard size. Let's assume there is zero evaporation of water. Single straw is used to draw water. 

What we Know: 

1. Volume of the bathtub: 6*3*3 = 72 cubic feet. Convert to meters. = 21 cubic meters = 2100 cubic cm.

2. Volume of straw =length = 20 cm, width = 0.5 cm or radius = 0.25 cm. The formula = (pi)* (r)*(r) * (h) = 20 * 0.0625* 3.14 = 3.4 or approx 4 cubic cm.

3. Time taken to fill and empty a straw = This seems like about 3 seconds to draw the water and empty elsewhere. 

Formula: 

No. of trips = (Volume of tub/volume of straw) 

= (21000000 / 4 )   = approx 500,000 trips

Next, let us look at how long it will take to execute this many trips. 

 = 5000000 * 3 = 1500000 seconds = 416 hours = 416/24 = 17 days.

Edge Cases: There may be partly filled pipe 5% of the time. THis may increase the time to 426 hours.