Okay, here is a site where they talk about how they convert land ice to sea level rise, so I'll apply those calculations and just use the swimming pool equivalent -
To convert a mass of ice into the total amount global sea levels would rise if the ice all melted (i.e., the sea level equivalent), we need to know how much area the oceans cover. This is usually given as 3.618 x 108 km2. A 1 mm increase in global sea level requires 10-3 m3 (10-12 km3) of water for each square metre of the ocean surface, or 10-12 Gt of water.
We can calculate the volume of water required to raise global sea levels by 1 mm:
Volume = area x height
Area = 3.618 x 108 km2
Height = 10-6 km (1 mm)
Volume (km3) = (3.618 x 108 km2) x (10-6 km) = 3.618 x 102 km3 = 361.8 km3 water.
antarcticglaciers.org: Calculating glacier ice volumes and sea level equivalents
So, we need 361.8 cubic kilometers to raise sea levels 1 mm.
25.4 mm = 1 inch
152.4 mm = 6 inches
So, we need 152.4 x 361.8 cubic kilometers of additional water to raise sea levels 6 inches.
= 55,138.32 cubic kilometers.
1 cubic kilometer = 1000 meters x 1000 meters x 1000 meters = 1 billion cubic meters.
So we need 55,138,320,000,000 (55+ trillion) cubic meters.
How much water in an Olympic sizes swimming pool?
An Olympic course (minimum needed to officially host an Olympic event) is 50 meters in length, 25 meters wide, at least 2 meters deep, but recommended minimum depth is 3 meters (the FINA.org website is down for some reason, so I had to use other sources).
Length is 164 feet (50 meters) Width: 82 feet (25 meters) Depth: 7 feet; 2 meters (minimum); 9 feet, 10 inches (3 meters) is recommended. Pools for Olympic Games and World Championships must be equipped with flush walls at both ends.
the Spruce: How big is an Olympic-sized swimming pool?
Both 2012 London and 2008 Beijing Olympic pools are 3M deep. (Wikipedia: London Aquatics Centre)
50 meters x 25 meters x 3 meters = 3750 cubic meters.
55.13832 x 1012 / 3750 = 14,703,552,000 Olympic-sized swimming pools to raise the oceans by 6 inches.
2100 - 2018 (since the century ends on December 31, 2100, and it is now October 2018, I will just use those numbers for years) = 82 years.
82 years x 365 days = 29,930 days
plus 20 leap days = 29,950 days
x 24 = 718,800 hours
x 60 = 43,128,000 minutes
x 60 = 2,587,680,000 seconds
x 2 = 5,175,360,000 Olympic pools by the end of the century.
the volume needed divided by the volume of the analogy = 2.84, or only 35% of the volume needed, using recommended depth instead of minimum.
Keep in mind it's a rough comparison, he says it's discharging "more than," Olympic sized pool dimensions can vary a lot, as long as they meet the minimum standards, and "could cause as much as" - a lot of conditional and hedged language used.
But, if we are evaluating the quality of the analogy by seeing if a constant rate of two standard Olympic venue pools per second can raise the oceans by 6 inches in 82 years, it seems that it falls well short.
If we ignore the swimming pool analogy, then we need the current melt rate, some other way. I looked for the date of the lined article (current, Oct 15, 2018) so I looked for our current rate. I found several articles where they reference that the melt rate for the Antarctic ice sheet has tripled, vs either ten or 25 years ago.
Between 1992 and 2017, Antarctica shed three trillion tons of ice. This has led to an increase in sea levels of roughly three-tenths of an inch, which doesn’t seem like much. But 40 percent of that increase came from the last five years of the study period, from 2012 to 2017.
NY Times: Antarctica Is Melting Three Times As Fast As A Decade Ago
If you go by what's stated in the paragraph, it seems like a trillion tons of melt corresponds to 1/10 of an inch.
40% of 3 trillion is 1.2 trillion over five years, a rate of 240 billion tons per year. By the NY Times estimate, that's .024 inches per year.
.024 x 82 years = 1.986 inches, again, just north of 30% of the six inch number cited.
Let's combine sources and see how 240 B tons per year translates using the more extensive calculations from our first source.
Because ice and water are different densities, 1 km3 results in different masses. However, remember that 1 Gt of ice = 1 Gt of water! They take up different volumes but have the same mass.
...... If we took our 458.30 Gt of ice (as calculated above), then we could calculate the global sea level equivalent by:
SLE (mm) = mass of ice (Gt) x (1 / 361.8)
SLE = 458.30 x (1 / 361.8)
SLE = 1.27 mm
1 Gt = 1 billion metric tons.
The mass of ice to raise sea level by 1mm is 360.8661 Gt (458.3/1.27)
Again, 6 inches = 152.4 mm
So we need 360.8661 billion metric tons x 152.4 mm for a six inch sea level rise.
That comes to just a hair under 55 trillion metric tons (54,996,000,000,000).
If we assume they were using metric units for the melt rate, then it would take 229.15 years, at 240 billion tons per year. 82 (years) is 35% of 229.
That number matches the above "swimming pool" calculations.
I guess the next edit will be after looking at what the scientists said, instead of how the reporters reported it, when they refer to the "rate" - because it doesn't seem like a constant for the past five years gets anywhere close to that, but it is accelerating rapidly. I'm more inclined to think that the reporting is imprecise vs the scientists missing by a factor of almost three when some jamoke on a stackexchange can calculate that out.
So, the claim, as reported by the media, does not seem to hold up. Whether the claim as reported matches the claim made by scientists is another matter for inquiry.