The 'Giants' wiped out in the flood were the Nephilim (from root n-f-l - fallen) :
genesis 6:4
There were giants (Nephilim) in the earth in those days; and also after that, when the sons of God came in unto the daughters of men, and they bare children to them, the same became mighty men (Giborim) which were of old, men of renown.
On another note however, the 6-5 ritual notes:
2nd Ad. "Herein my Frater, you may perceive somewhat of the same symbolism under another and deeper signification than this, since the Hanged Man (under which title you may remember that our Lord was 'hanged upon a Tree') is also entitled the Drowned Giant, and in this likeness may be said to refer to the Adam Kadmon of the Kabbalists- the ideal man who reflects the Image of God, even as thy face was but now reflected in the bowl of water. And herein is a great mystery, for in each of us is submerged that Image, but oftentimes so distorted by the waves of the tempestuous passions that it is unrecognizable, save to the discerning eye of the Adept, whose vocation it is to utter the word of Power: 'Peace; be still.' In the act of Creation, it may be said that the Supreme sacrificed Himself by imposing certain limits; thereby He was thenceforward bound in manifestation, even as the Word conformed to the limitations of Humanity in His Incarnation. Therefore, must we also offer ourselves as a living sacrifice; holy, acceptable unto God, which is our reasonable service. The 22nd Path of Mem is called the Faithful Intelligence, and it is so called because by it, spiritual virtues are increased and all dwellers upon Earth are nearly under its shadow."
Waite in the rituals of the FRC calls the great symbol the Crowned Master, but also the Crowned Titan (which would link in the GD description as Giant - tribes of the Giants after the flood were referred to as Titans).
"The Crowned Titan, who was shewn to you in the Path of MEM, submerged beneath the Waters of Creation and in the deeps within your own nature...,"